The present invention relates to a graphical measuring device to simplify the operation of measuring electrical signals.
An oscilloscope is a device which displays a graph of voltage or current over time. In order to display meaningful information, the oscilloscope must be configured to measure voltage or current over a meaningful range of magnitudes during a proper time duration. The start of the time period for measuring voltage or current must be selected by choosing a proper triggering event based on the anticipated electrical signal to be measured. The triggering event may include the trigger level voltage and the trigger slope. For example, a triggering event could be a voltage signal rising above 0.1 volts. The time duration and voltage range should be selected so that a full electrical signal (waveform) is visible on the display. To make a meaningful interpretation of the displayed waveform, the user must know what the waveform should look like.
For example, if the user is measuring a square wave signal that varies between 0.01 volts to 0.06 volts every 100 microseconds, then it would be useless to view the square wave signal on a voltage scale set to display signals between 0 to 0.005 volts. Also, it would not be optimal to measure the square wave signal over a time duration of 10 microseconds. Further, if the triggering event was set to sense an increasing signal greater than 0.1 volts, then the square wave signal would never trigger the device and hence no waveform would be displayed. It is apparent that to simply make a proper measurement, the user must select the scaling, time duration, trigger level voltage, and the trigger slope, all for an electrical signal for which the user presumably has a prior knowledge of its characteristics. If the user does not know or can recall the anticipated signal's characteristics then the process to properly sense and display a waveform requires experimentation in an attempt to set all parameters. This experimentation may require considerable time and be frustrating to the user.
For the aforementioned example, a properly configured measuring device should have the voltage scale range set to 0 to 0.1 volts to permit viewing the height of the entire waveform. The time period should be set to either 500 or 1000 microseconds so that at least one entire waveform time period is displayed. The triggering event could be selected to trigger with an increasing voltage over 0.015 volts, which is above the minimum anticipated voltage of 0.01 volts. The trigger slope, if needed, would be set accordingly.
Many technicians, including automobile technicians, are likely to be unfamiliar and untrained with respect to the proper operation of such an oscilloscope. With all their other concerns, it is a time consuming burden for such technicians to be properly trained to correctly configure an oscilloscope to perform various tests and measurements. In particular for automotive technicians, many tests have become necessary with the advent of microchip controllers within automobiles.
A traditional desktop oscilloscope may be used by technicians to display measurements for testing and troubleshooting. However, as previously explained, many technicians may be unfamiliar with the proper operation of an oscilloscope. Further, it is burdensome for the technician to move desktop oscilloscopes to remote testing locations to take measurements.
Fluke Corporation of Everett, Washington, has designed and is marketing a handheld 860 series GMM (Graphical Multimeter) that displays electrical waveforms in a manner similar to that of a desktop oscilloscope. However, unlike an oscilloscope, the 860 series GMM is not capable of sampling at over 100,000 Hz which provides an inadequate sampling rate for many applications. In essence, the graphical multimeter is best at sensing the general trends of electrical signals. In general, oscilloscopes sample at rates in excess of 1 MHz and thereby can display transients of electrical signals that the 860 series GMM, and similar graphical meters, are incapable of doing. Most oscilloscopes operate at frequencies of 5 MHz or more. Like an oscilloscope, Fluke's 860 series GMM is complicated to configure, particularly when used by an untrained technician unfamiliar with its operation. Accordingly, for technicians, and in particular automobile technicians, a graphical measuring device that is easy to configure to perform tests and measurements is desirable. Furthermore, if the technician does manage to properly configure the measuring device, the technician may still be unable to interpret the meaning of the waveform, for example, whether or not the waveform indicates the existence of a problem, without prior knowledge of how a proper waveform should appear.
Olsen U.S. Pat. No. 3,789,658 discloses an automobile engine performance analyzer which includes an oscilloscope and three selectable scale test meters for displaying certain operating characteristics of an engine under test. In particular, a program switch is provided with a rotary selector knob for positioning the switch at any selected position for measuring and displaying one of the characteristics A-L. However, the oscilloscope uses the same scaling of the graphical display for all the different tests. This does not allow optimum viewing of all waveforms (if any waveform is displayed at all), because each waveform may have a different magnitude, time duration and trigger point.
What is desired, therefore, is an interface for a graphical display device that frees the user from setting the scaling, time duration, trigger level voltage, and trigger slope for one or more user-selected tests. Furthermore, the display device should assist the user in determining whether the displayed waveform is correct.